Valve unit for a piston compressor and piston compressor

ABSTRACT

A valve unit for a piston compressor includes a housing, in which at least one inlet valve and at least one outlet valve are arranged. The housing includes a first cylinder-head-side surface and a second, cylinder-side surface which is away from the first cylinder-head-side surface. The surfaces extending transversely to a longitudinal axis of the valve unit. A peripheral wall of the housing of the valve unit, and which surrounds the longitudinal axis of the valve unit, includes at least one contact section. The at least one contact section is provided for contact on a contact surface on the cylinder or on the cylinder head and extends obliquely to the longitudinal axis.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority under 35 U.S.C. §119 of European patent application 161 64 389.5, filed Apr. 8, 2016, the entire contents of which are incorporated herein by reference.

FIELD OF THE INVENTION

The invention relates to a valve unit for a piston compressor, as well as to a piston compressor.

BACKGROUND OF THE INVENTION

In the general case, piston compressors are provided with valve units which there are usually arranged in the region of an interface of a cylinder with a cylinder head and fastened between the cylinder and the cylinder head. The valve units serve for forming a closable flow connection from a gas inlet arranged on the cylinder head to the inside of the cylinder and for forming a flow connection from the inside of the cylinder to a gas outlet arranged on the cylinder head, the latter-mentioned flow connection being closable independently of the first-mentioned flow connection. The general construction of a valve unit for a piston compressor and belonging to the state of the art is hereinafter explained by way of FIG. 8, which shows an example of a known valve unit.

The valve unit which is represented in FIG. 8 comprises a housing which in the present case is designed in a two-part manner, specifically is formed by two cylindrical valve bodies which is to say housing parts 2 and 4 which are arranged above one another in the direction of a longitudinal axis A of the valve unit and which are connected to one another by way of screw 6. One or more inlet valve cross sections 12 which is to say inlet valve channels 12 with one or more inlet valves 12 which are arranged therein and one or more outlet valve cross sections 14 which is to say outlet valve channels 14 with one or more outlet valves 15 which are arranged therein, are arranged in the housing of the valve unit, between a surface 8 of the housing part 2 which faces the cylinder of the piston compressor in the installed position of the valve unit in a piston compressor, and a surface 10 of the housing part 4 which is away from the surface 8 and which faces the cylinder head of the piston compressor in the installed position of the valve unit in the piston compressor. Such inlet valves 13 and outlet valves 15 can be designed as disc valves or reed valves in the manner known per se. The inlet valves 13 and the outlet valves 15 in this case which is shown in FIG. 8 are each designed as spring-disc valves, wherein the inlet valve cross sections 12 release a flow path through the housing of the valve unit from outside the surface 10 of the housing part 4 to outside the surface 8 of the housing part 2, and the outlet valve cross sections 14 in the reverse direction release a flow path through the housing of the valve unit from outside the surface 8 of the housing part 2 to outside the surface 10 of the housing part 4. The housing part 2 has a greater diameter compared to the housing part 4 and thus forms an annular, radial widening 16 of the housing of the valve unit. In the installed position of the valve unit in a piston compressor, the fixation of the valve unit between the cylinder and the cylinder head is effected in the region of this widening 16, wherein the housing part 2 engages into a cylindrical recess which is formed on the cylinder or on the cylinder head. The recess is hereby dimensioned such that the housing part 2 is positively fixed in the recess in the radial direction.

During operation of the piston compressors, the valve units which are built into these are subjected to considerable wear. This amongst other things is due to the valve units being exposed to a significant thermal loading on account of the heat which arises with the compression of gases. The wear occurring on the valve units renders it necessary to regularly disassemble the valve units from the piston compressors and to replace them with new valve units. Hereby, it is above all the disassembly of the valve unit from the piston compressor which has been found to be problematic, since the region of the valve unit which engages into the recess formed on the cylinder or the cylinder head can become very firmly stuck in the recess due to a possible corrosion and/or coking which has previously taken place between the valve unit and the recess.

SUMMARY OF THE INVENTION

Against this background, it is an object of the invention to provide a valve unit for a piston compressor, the unit ensuring an improved heat dissipation from the valve unit and being able to be simply removed from a piston compressor and simply installed into a piston compressor. A further object of the invention lies in providing a piston compressor which is improved with regard to the mentioned aspects.

According to the invention, a valve unit for a piston compressor is provided with a cylinder an with a cylinder head. The valve unit comprises a housing, in which at least one inlet valve and at least one outlet valve are arranged. The housing comprises a first, cylinder-head-side surface and a second, cylinder-side surface which faces away from the first, cylinder-head-side surface. The first, cylinder-head-side surface and the second, cylinder-side surface extend transversely to a longitudinal axis of the valve unit. A peripheral wall, which surrounds the longitudinal axis of the valve unit, comprises at least one cylinder or cylinder head contact section for contact on the cylinder or the cylinder head. The cylinder or cylinder head contact section extends obliquely to the longitudinal axis.

The valve unit according to the invention is provided, designed or adapted for application in a piston compressor. It comprises a housing, in which at least one inlet valve and at least one outlet valve are arranged. Typically, also more than one inlet valve and more than one outlet valve can be arranged in the housing under certain circumstances. The valves can be designed e.g. as disc valves or reed valves, in the manner known per se. The housing has a surface at the cylinder head side, i.e. a surface which faces a cylinder head of the piston compressor in the installed position of the valve unit in a piston compressor, and has a surface at the cylinder side, said surface being away from the cylinder-head-side surface, i.e. a surface which faces a cylinder of the piston compressor in the installed position of the valve unit in a piston compressor. The cylinder-head-side surface and the cylinder-side surface of the housing extend transversely and in particular normally to a longitudinal axis of the valve unit. The at least one inlet valve and the at least one outlet valve, between the cylinder-side surface and the cylinder-head-side surface are usefully arranged in the housing such that they create closable flow connections from outside the cylinder-head-side surface to outside the cylinder-side surface. A throughflow through the valve unit through the at least one inlet valve is effected from the cylinder-head-side surface to the cylinder-side surface and a throughflow through the valve unit through the at least one outlet valve is effected in a direction reverse to this.

The valve unit according to the invention, compared to the valve units for piston compressors and which have been known until now, is characterized that a peripheral wall of the housing of the valve unit and which surrounds the longitudinal axis of the valve unit comprises at least one contact section (cylinder or cylinder head contact section) provided for bearing contact on a contact surface on the cylinder or cylinder head, of a piston compressor and extending obliquely to the longitudinal axis of the valve unit. Preferably, a contact surface which is formed on the cylinder or on the cylinder head is adjacent the complete peripheral wall of the valve unit in the installed condition, wherein the peripheral wall formed on the valve unit, at least in a peripheral region which according to the invention is indicated as the contact section, tapers to the longitudinal axis of the valve unit, preferably at an acute angle. The contact surface which is formed on the cylinder or on the cylinder head, in a corresponding peripheral section preferably tapers to the longitudinal axis of the valve unit at the same angle as the contact section of the valve unit. The peripheral wall of the valve unit which forms the contact section, although preferably being directly part of the housing of the valve unit, however it is to be noted that this peripheral wall can also be formed by a component which is separate from the housing, such as e.g. by a ring element, which for example in a manner in which it is connected to the housing, surrounds the housing at the outer side or is recessed in the housing. In the context of the invention, such a separate component also forms a part of the housing of the valve unit, i.e. the housing of the valve unit is thus designed in a multi-part manner.

Some significant advantages result in combination with the compressor-side contact surface which corresponds to the peripheral wall of the housing of the valve unit, with regard to which an inclination corresponding to the inclination of the contact section is formed on at least one section. One of these advantages lies in the fact that on account of its inclination to the longitudinal axis of the valve unit, the at least one contact section of the peripheral wall of the housing of the valve unit creates a greater contact region between the valve unit and the adjacent parts of the piston compressor compared to contact surfaces running parallel to the longitudinal axis as with the valve units which have been known until now, and this permits an increased heat dissipation from the valve unit into the housing of the piston compressor which surroundings this valve unit, which is to say into the outer environment of the piston compressor, compared to those valve units which are known from the state of the art. The thermal loading of the valve unit is thus reduced, which in turn has a favorable effect on the service life of the valve unit. Apart from the improved heat dissipation out of the valve unit, the at least one obliquely aligned contact section formed on the peripheral wall of the housing of the valve unit also effects an improved force transmission between the valve unit and the piston compressor, on fixation of the valve unit on a piston compressor. Moreover, the disassembly of the valve unit out of a piston compressor is simplified by way of the inventive design of the peripheral wall of the housing of the valve unit, with the contact section which is formed thereon, since here, the peripheral wall of the housing of the valve unit, at the at least one obliquely aligned contact section, is not moved parallel to the contact surface of the piston compressor which is adjacent the peripheral wall, as is the case with the valve units know until now, but given a movement of the valve unit in the direction of its longitudinal axis, is moved directly away from the compressor-side contact surface, so that the entire valve unit can detach immediately from corrosion or coking substances or other contamination, which as the case may be are situated between the peripheral wall of the valve unit and the compressor-side contact surface.

Preferably, the housing of the valve unit according to the invention has a round and in particular circular basic shape, wherein the longitudinal axis defines the middle axis of this outer contour. This means that the housing at least with regard to its geometric basic shape preferably has a round and particularly preferably a circular cross section, essentially over its entire length in the direction of the mentioned longitudinal axis, wherein the cross section of the housing further preferably at most deviates from this basic cross-sectional shape in the region of a contact section, given a contact section which is formed on the outer periphery of the housing. Hereby, the housing can comprise several housing parts with a different cross-sectional size, e.g. on account of one or more shoulders formed on the housing, wherein however all these housing parts preferably have a round and in particular circular basic shape and wherein these housing parts preferably have a common middle axis in the form of the mentioned longitudinal axis.

According to a further preferred development of the invention, the contact section which is provided on the peripheral wall of the housing of the valve unit extends over one or more peripheral sections of the peripheral wall. This means that the contact section running obliquely to the longitudinal axis of the valve unit preferably extends only over a part-region of the peripheral wall in the peripheral direction of the peripheral wall, which is to say that the peripheral wall comprises several regions which are distanced to one another in the peripheral direction of the peripheral wall and which are aligned obliquely to the longitudinal axis of the valve unit. This design is particularly useful if the valve unit is to be installed in the piston compressor in a plane normal to the longitudinal axis of the valve unit in a designated angular alignment. If the compressor-side contact surface comprises one or more locally defined sections with an inclination which is formed in a manner corresponding to the contact sections of the valve unit, then one can succeed in the valve unit only being able to be installed into the compressor at a defined angular position.

Furthermore, one preferably envisages the described oblique contact section extending over the entire periphery of the peripheral wall of the housing of the valve unit, as an alternative to one or more contact sections extending only over a peripheral section of the peripheral wall of the valve unit. I.e. in this case, a region which is aligned obliquely to the longitudinal axis of the valve unit is provided on the peripheral wall over the complete periphery. This measure permits a particularly efficient heat dissipation from the valve unit to the housing of the piston compressor and a gas-tight sealing of the valve unit with respect to the contact surface formed on the cylinder or on the cylinder head, of the piston compressor, wherein it is to be pointed out that it can be useful or indeed necessary to seal the valve unit with respect to the cylinder and with respect to the cylinder head, by way of further separate seals.

The angle, at which the contact section extends obliquely to the longitudinal axis of the valve unit can advantageously be constant over a peripheral extension of the contact section. Accordingly, with this design, the peripheral wall of the housing of the valve unit tapers with the same gradient in a straight direction obliquely to the longitudinal axis of the valve unit, over its complete periphery, which is advantageous in particular with regard to manufacturing technology. However, designs with which the angle of inclination of the contact section changes in a stepwise or continuous manner over the periphery are also conceivable.

The contact section of the valve unit can advantageously be situated on an outer peripheral wall or on an inner peripheral wall, of the housing. Accordingly, e.g. a region of an outer peripheral wall of the housing can be aligned obliquely to the longitudinal axis of the valve unit, for forming the contact section, wherein a compressor-side contact surface then surrounds the contact section of the housing of the valve unit at the outer periphery. Alternatively or additionally, a recess which runs in the direction of the longitudinal axis of the valve unit and whose inner peripheral wall is aligned obliquely to the longitudinal axis of the valve unit can also be formed on the valve unit, wherein in this case a compressor-side contact surface is adjacent the inner peripheral wall at the inner side of the inner peripheral wall.

Further preferably, the contact section of the peripheral wall of the housing of the valve unit is formed by a conical surface and/or by a surface which is arcuate in a plane transverse to the peripheral direction, i.e., e.g. has the outer contour of an ellipsoidal or spherical segment. Thus, with regard to a contact section provided on an outer wall of the housing of the valve unit, a region of the housing can form a truncated cone, wherein the lateral surface of this truncated cone forms the contact section, or a recess which is in the form of a truncated cone and whose inner peripheral wall forms the contact section can be formed on the housing of the valve unit. With the design, with which the contact section of the valve unit is formed by a surface which has the outer contour of an ellipsoidal or spherical segment, the contact sections comprises a curvature in a plane parallel to the longitudinal axis of the valve unit. In particular, such a design can be applied when the contact section is situated on an outer peripheral wall of the housing of the valve unit, e.g. on the outer peripheral wall and departing from an apex line which is radially distanced furthest to the longitudinal axis of the valve unit, an annular outer surface can be arched in the direction of the longitudinal axis of the valve unit, in an axial direction or in opposite axial directions.

According to a further advantageous further development of the valve unit according to the invention, the angle and/or the curvature, at which the contact section extends obliquely to the longitudinal axis is selected such that a self-locking does not occur given bearing contact on a contact surface extending in a parallel manner. This means that the angle, at which the contact section is aligned obliquely to the longitudinal axis of the valve unit is dimensioned in dependence on the surface nature of the contact section of the valve unit and on the compressor-side contact surface, in a manner such that no static/adhesive friction causing a self-locking can occur between the contact section and the contact surface. This is significant inasmuch as a simple disassembly of the valve unit out of the piston compressor is likewise ensured by way of this measure.

While specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is hereinafter explained in more detail by way of embodiment examples represented in the drawings. In the drawings:

FIG. 1 is a perspective exploded representation of a part of the piston compressor;

FIG. 2 is the representation according to FIG. 1, in a sectioned view,

FIG. 3 is a sectioned view, the part of a piston compressor which is represented in FIGS. 1 and 2, in the assembled condition;

FIG. 4 is a sectioned view, a part of a piston compressor according to a second embodiment;

FIG. 5 is a sectioned view, a part of a piston compressor according to a third embodiment;

FIG. 6 is a sectioned view, a part of a piston compressor according to a fourth embodiment;

FIG. 7 is a sectioned view, a part of a piston compressor according to a fifth embodiment; and

FIG. 8 is a sectioned view, a valve unit of a piston compressor which belongs to the state of the art.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the drawings a piston compressor is represented in parts in FIG. 1-3. This piston compressor comprises a cylinder 18, in whose interior 20 a piston is guided in a linearly movable manner. The representation of the piston and its drive has been omitted in the drawings for reasons of a better overview, since the piston and its drive are not essential to the invention and the piston as well as piston drives of piston compressors has been known for some time now from the state of the art. The cylinder 18 is closed at one end by a cylinder head 22. Here, in this example, the cylinder head 22, lying on a side 24 of the cylinder 18, is screwed to the cylinder 18 via four threaded pins 26. The cylinder head 22 however could also be connected to the cylinder 18 in another manner, for example via more or less than four threaded pins 26.

A valve unit 28 is arranged in the piston compressor, between the cylinder 18 and the cylinder head 22. A housing 30 of this valve unit 28 is designed in a stepped manner. The housing 30 is thereby designed in a two-part manner, from a first housing part 32 and a second housing part 34, wherein a first housing part 32 is radially widened or extended compared to a second housing part 34 which connects onto the first housing part 32 in a direction of a longitudinal axis A of the valve unit 28, and thus has a larger cross section than the second housing part 34. As a whole, the valve unit 28 with regard to is basic construction can correspond to the construction according to FIG. 8, wherein the housing part 32 corresponds to the housing part 2 in FIG. 8, and the housing part 34 corresponds to the housing part 4 in FIG. 8. Both housing parts 32 and 34 have a circular outer contour. The housing parts 32 and 34 are suitable for being connected to one another, but can also be designed in a single-part manner. At least one inlet valve and one outlet valve are arranged in the housing 30 of the valve unit 28, in a cross-sectional region of the housing 30 which is delimited by the cross-sectional contour of the housing part 34. The at least one inlet valve and the at least one outlet valve have been omitted in the drawings in each case for reasons of a better overview, but can for example also be designed in the same manner as the valve unit which is represented in FIG. 8 and which belongs to the state of the art. With all valve units 28 which are represented in the drawings, the at least one inlet valve 12 forms a closable flow path through the valve unit 28, running from a surface 36 of the housing 30 to a surface 38, and the at least one outlet valve 14 forms a closable flow path through the valve unit 28, running from the surface 38 of the housing 30 to the surface 36.

With its arrangement between the cylinder 18 and the cylinder head 22 of the piston compressor represented in FIG. 1-3, the valve unit 28 engages into a recess 40 of the cylinder head 22 which is formed on a side 42 of the cylinder head 22 which faces the cylinder 18 and is arranged there in a manner such that the longitudinal axis A of the valve unit 28 engaging into the recess 40 corresponds to a longitudinal axis B of the piston compressor or the cylinder head 22. The recess 40 is radially widened compared to the interior 20 of the cylinder 8, i.e. the recess 40 has a larger diameter compared to the interior 20.

In the cylinder head 22, the housing 30 of the valve unit 28 is supported in a gastight manner on a flow channel 48 which is formed there, via a sealing ring 44 which engages into a recess 46 formed on the surface 36 of the housing part 34. The flow channel 48 which in the cylinder head 22 is arranged coaxially to the longitudinal axis B of the piston compressor, which is to say coaxially to the longitudinal axis A of the valve unit 28, projects on the outer side of the cylinder head 22 which is away from the cylinder 18, and there this flow channel forms a gas inlet of the piston compressor. Gas which is to be compressed in the piston compressor can flow from this gas inlet into the interior 20 of the cylinder 18 via the at least one gas inlet valve 12 arranged on the valve unit 28.

The at least one gas outlet valve 14 of the valve unit 28 is arranged on the valve unit 28, radially to the outside on the recess 46 formed on the housing 30 of the valve unit 28 and is flow-connected to an annular space 50 which is formed in the cylinder head 22 and which surrounds the flow channel 48 at the outer periphery. The annular space 50 is flow-connected to a gas outlet 52 of the piston compressor which is formed on the cylinder head 22, so that compressed gas in the interior 20 of the cylinder 18 can get to the gas outlet 52 via the at least one outlet valve of the valve unit 28 and via the annular space 50.

An outer peripheral wall 54 of the housing part 32 contacts a peripheral wall 56 of the recess 40, with the engagement of the housing 30 of the valve unit 28 into the recess 40 formed on the cylinder head 22. Accordingly, the outer peripheral wall 54 forms a contact section of the valve unit 28 which comes into bearing contact on a contact surface (valve unit contact surface) formed by the peripheral wall 56 of the recess 40.

The outer peripheral wall 54 of the housing part 32, over its entire peripherally about the longitudinal axis A, extends at a constant angle obliquely to the longitudinal axis A of the valve unit 28 in a direction away from the cylinder 18. The housing part 32 of the valve unit 28 thus has a conical shape or the shape of a truncated cone, wherein the cross section of the housing part 32 reduces in the direction of the cylinder head 22. The peripheral wall 56 over its entire periphery is also aligned obliquely to the longitudinal axis A of the valve unit 28 at the same constant angle as the outer peripheral wall 54, indeed in a manner corresponding to this outer peripheral wall 54, wherein the peripheral wall 56 tapers obliquely to the longitudinal axis A of the valve unit 28 in a direction away from the cylinder 18. The peripheral wall 56 also has a conical shape. With the engagement of the housing 30 of the valve unit 28 into the recess 40 of the cylinder head 22, the outer peripheral wall 54 of the shoulder 32 of the housing 30 thus bears on the peripheral wall 56 of the recess 40 over the complete surface. The magnitude of the angle, at which the outer peripheral wall 54 of the housing part 32 of the valve unit 28 as well as the peripheral wall 56 of the recess 40 of the cylinder head 22 is aligned obliquely to the longitudinal axis A of the valve unit 28, is preferably such that essentially no self-locking or jamming can occur between the housing 30 engaging into the recess 40 and the recess 40.

It is to be understood that the outer peripheral wall of the second housing part 34, alternatively or additionally could also be aligned conically or obliquely to the longitudinal axis A of the valve unit 28, in a manner corresponding to the outer peripheral wall 54. A contact surface (valve unit contact surface) for the outer peripheral wall of the housing part 34 could then be formed in the cylinder head, similarly to the design of the peripheral wall 56.

With this engagement of the housing part 32 into the recess 40 of the cylinder head 22, the housing 30 moreover bears on an annular shoulder 60 via a surface 58 of the housing part 32 which is away from the surface 38. The shoulder 60, at that end of the peripheral wall 56 of the recess 40 which is away from the cylinder 18 extends transversely to the longitudinal axis A of the valve unit 28 in the direction of the longitudinal axis A and narrows the cross section of the recess 40 to the cross section of the housing part 34. On assembly of the cylinder head 22 on the cylinder 18, the cylinder head 22, with the valve unit 28 whose surface 38 is flush with the side 40 of the cylinder head 22 is placed onto the side 24 of the cylinder 18 and is screwed to the cylinder 18, wherein an annular flat seal 62 is previously arranged on the side 24 of the cylinder 18, said seal sealing the cylinder 18 with respect to the valve unit 28 and to the cylinder head 22 as well as the surroundings or atmosphere, in a gas-tight manner.

FIG. 4 shows a piston compressor which merely differs from the piston compressor represented in FIG. 1-3 with regard to the design of the cylinder head, wherein the cylinder 18 and the valve unit 28 of the piston compressor represented in FIG. 4 is identical to the cylinder 18 and the valve unit 28 of the piston compressor represented in FIG. 1-3. The cylinder head 22′ of the piston compressor 22 represented in FIG. 4 largely corresponds to the cylinder head 22 of the piston compressor represented in FIGS. 1-3, wherein the single difference between the cylinder head 22′ and the cylinder head 22 lies in the fact that with the cylinder head 22′, the shoulder 60 provided in the case of the cylinder head 22 has been omitted and a peripheral wall 56′ of the recess 40′ of the cylinder head 22′ extends obliquely in the direction of the longitudinal axis A of the valve unit 28 in a direction away from the cylinder 18, wherein the peripheral wall 56′ ends directly at the annular space 50 of the cylinder head 22′. The valve unit 28 in the region of its outer periphery therefore only bears on the cylinder head 22′ via the peripheral wall 54.

The piston compressor which is represented in FIG. 5 comprises a cylinder head 22′ which is identical to the cylinder head 22′ of the piston compressor represented in FIG. 4. A cylinder 18′ of the piston compressor represented in FIG. 5 largely corresponds to the cylinder head 18 of the piston compressor represented in FIG. 1-3. The cylinder 18′ however differs from cylinder 18 to the extent that a recess 64 forming a radial widening of the interior 20 of the cylinder 18′ is formed on its side 24 facing the cylinder head 22′. A peripheral wall 66 which radially delimits the recess 64 is configured in a manner such that in a direction away from the cylinder head 22′, its tapers obliquely to the longitudinal axis A of a valve unit 28′ provided in the piston compressor. The peripheral wall 66 thus likewise has a conical shape. Hereby, an end of the peripheral wall 66 which faces the cylinder head 22′ is flush with the end of the peripheral wall 56 of the recess 40′formed on the cylinder head 22′, said end facing the cylinder 18′. The valve unit 28′ differs from the valve unit 28 which is represented in FIGS. 1-4, only with regard to the design of the housing part 32′. The housing part 32′ comprises an outer peripheral wall 54′ which, from a plane 68 situated essentially centrally between a surface 38′ and a surface 58′ of the housing part 32′, in a region facing the cylinder head 22′ tapers to the longitudinal axis A of the valve unit 28 in a direction way from the cylinder 18′ and in a region facing the cylinder 18′ tapers to the longitudinal axis A of the valve unit 28′ in a direction away from the cylinder head 22′. The outer peripheral wall 54′ thus has the shape of a double cone which departing from the middle tapers to both axial ends. The angle, at which the outer peripheral wall 58′, in its region facing the cylinder head 22′ tapers to the longitudinal axis A, corresponds to the angle, at which the peripheral wall 56 of the recess 40′ formed on the cylinder head 22′ tapers to the longitudinal axis of the valve unit 28′, whereas the angle, at which the outer peripheral wall 58′ in its region facing the cylinder 18′ tapers to the longitudinal axis A corresponds to the angle, at which the peripheral wall 66 of the recess 64 formed on the cylinder 18′ tapers to the longitudinal axis A. The housing part 32′, with the region facing the cylinder 18′ engages into the recess 64 formed on the cylinder 18′, wherein the region of the housing part 32′ which faces the cylinder head 22′ is received by the recess 40′ which is formed on the cylinder head 22′. In this position, the valve unit 28′ is fixed in the piston compressor, between the cylinder 18′ and the cylinder head 22′.

The piston compressor which is represented in FIG. 6 has the same cylinder 18′ as the piston compressor represented in FIG. 5. A cylindrical recess 40″ running out into the annular space 50 is formed on a cylinder head 22″ of the piston compressor in a manner departing from the side facing the cylinder 18′. The diameter of the recess 40″ is smaller than the largest diameter of the recess 64 formed on the cylinder 18′. A valve unit 28″ with its housing part 32″ engages into the recess 64. An outer peripheral wall 54″ of the housing part 32″ over its entire periphery tapers obliquely to the longitudinal axis A of the valve unit 28′ in a direction away from the cylinder head 22″ in a manner corresponding to the peripheral wall 66 of the recess 64 of the cylinder 18′. The housing part 32″ in the direction of the longitudinal axis A is dimensioned such that a surface 58″ of the housing part 32″ is flush with the side 24 which is to say the axial end-face 24 of the cylinder 18′. A part of the wall of the cylinder head 22″, said wall radially surroundings the recess 40″ of the cylinder head 22″, lies on the surface 58″ of the housing part 32″, so that the valve unit 28″ is fixed between the cylinder 18′ and the cylinder head 22″.

The piston compressor which is represented in FIG. 7 comprises a cylinder 18″ which only differs from the cylinder 18 of the piston compressor represented in FIGS. 1-3 in that a recess 72 extending over the entire outer periphery 70 is formed on the outer periphery 70 of the cylinder 18″ in a manner adjacent the side 24 of the cylinder 18″. An outer peripheral wall 74 of the recess 72 tapers obliquely to a longitudinal axis A of a valve unit 28″' of the piston compressor, in the direction of the cylinder head 22″, i.e. has a conical shape. The cylinder head 22″ is identical to the cylinder head 22″ of the piston compressor represented in FIG. 6. The valve unit 28″ is characterized in that a housing part 32″' of the valve unit 28″' has a diameter which corresponds to the outer diameter of the cylinder 18″, in the region which is adjacent the recess 72, wherein a projection 76 in the form of an annular collar engaging into the recess 72 formed on the cylinder 18″ is formed on a surface 38″ facing the cylinder 18″, in a manner projecting in the direction of the longitudinal axis A. Here, an inner peripheral wall 78 of the projection 76 which has an inclination corresponding to the inclination of the peripheral wall 74 of the recess 72 and tapers obliquely in the direction of the cylinder head 22″ comes into contact with the peripheral wall 74 of the recess 72 of the cylinder 18″. 

What is claimed is:
 1. A valve unit for a piston compressor with a cylinder an with a cylinder head, the valve unit comprising a housing, in which at least one inlet valve and at least one outlet valve are arranged, the housing comprising: a first, cylinder-head-side surface; a second, cylinder-side surface which faces away from the first, cylinder-head-side surface, the first, cylinder-head-side surface and the second, cylinder-side surface extending transversely to a longitudinal axis of the valve unit; and a peripheral wall which surrounds the longitudinal axis of the valve unit, the peripheral wall comprising cylinder or cylinder head contact section for contact on the cylinder or the cylinder head, the cylinder or cylinder head contact section extending obliquely to the longitudinal axis.
 2. A valve unit according to claim 1, wherein the housing comprises a round outer contour, wherein the longitudinal axis defines a middle axis of this outer contour.
 3. A valve unit according to claim 1, wherein the cylinder or cylinder head contact section extends over one or more peripheral sections of the peripheral wall.
 4. A valve unit according to claim 1, wherein the cylinder or cylinder head contact section extends over a complete periphery of the peripheral wall.
 5. A valve unit according to claim 1, wherein an angle, at which the cylinder or cylinder head contact section extends obliquely to the longitudinal axis, is constant over a peripheral extension of the cylinder or cylinder head contact section.
 6. A valve unit according to claim 1, wherein the cylinder or cylinder head contact section is situated on an outer peripheral wall or an inner peripheral wall of the housing.
 7. A valve unit according to claim 1, wherein the cylinder or cylinder head contact section is formed by a conical surface or a spherical surface or by both a conical surface or a spherical surface.
 8. A valve unit according to claim 1, wherein an angle at which the cylinder or cylinder head contact section extends obliquely to the longitudinal axis is selected such that no self-locking occurs given a contact on a contact surface extending in a parallel manner.
 9. A valve unit according to claim 1, wherein: the housing, radially outwardly of the longitudinal axis, comprises a projection projecting in a direction of the longitudinal axis; the cylinder or cylinder head contact section is situated on a side of the projection which faces the longitudinal axis; and the projection is preferably configured as an annular collar, on whose inner periphery the cylinder or cylinder head contact section is situated.
 10. A piston compressor comprising: at least one cylinder and cylinder head connected to the cylinder; and a valve unit comprising a housing, in which at least one inlet valve and at least one outlet valve are arranged, the housing comprising: a first, cylinder-head-side surface; a second, cylinder-side surface which faces away from the first, cylinder-head-side surface, the first, cylinder-head-side surface and the second, cylinder-side surface extending transversely to a longitudinal axis of the valve unit; and a peripheral wall which surrounds the longitudinal axis of the valve unit, the peripheral wall comprising cylinder or cylinder head contact section for contact on the cylinder or the cylinder head, the cylinder or cylinder head contact section extending obliquely to the longitudinal axis.
 11. A piston compressor according to claim 10, wherein a valve unit contact surface with a contour corresponding to a contour of the cylinder or cylinder head contact section of the valve unit and which is in contact with the cylinder and/or cylinder head contact section of the valve unit is formed on the cylinder or on the cylinder head.
 12. A piston compressor according to claim 11, wherein the cylinder and/or the cylinder head comprises a recess into which the housing of the valve unit engages, wherein a peripheral wall of the recess forms the valve unit contact surface, with which the cylinder or cylinder head contact section of the valve unit is in contact.
 13. A piston compressor according to claim 12, wherein the recess is formed on a side of the cylinder head which faces the cylinder and/or on the side of the cylinder which faces the cylinder head, wherein the recess is a radial widening of an interior of the cylinder.
 14. A piston compressor according to claim 13, wherein the recess comprises a shoulder which is directed radially inwards transversely to the longitudinal axis and on which the housing of the valve unit bears.
 15. A piston compressor according to claim 11, wherein the valve unit contact surface for the contact section of the housing of the valve unit is formed on both the cylinder and on the cylinder head, wherein the contact surface which is formed on the cylinder head is aligned obliquely to the longitudinal axis and tapers obliquely in a direction away from the cylinder, wherein the contact surface formed on the cylinder, in at least in a peripheral section, is aligned obliquely to the longitudinal axis and tapers obliquely in a direction away from the cylinder head.
 16. A piston compressor according to claim 13, wherein the recess is formed on an end of the cylinder, which end faces the cylinder head, at an outer periphery of the cylinder. 